In a system of the type here contemplated, the local stations communicating with the exchange via respective radio links are connected through the usual line loops with radio transceivers individually assigned thereto; each transceiver and local station may be considered part of a peripheral installation associated with a central radio terminal which is directly linked with the exchange. A line repeater in each peripheral installation is designed to translate certain activating signals from the exchange, received via the associated radio link, into signals capable of being transmitted over the loop to operate certain equipment at the local station. In the case of a private subscriber, for example, an activating signal thus transmitted may be a command to generate ringing current; in the case of a pay station it may be a rate pulse instructing that station to collect a token or coin.
Conventional line repeaters associated with subscriber stations are, therefore, provided with alternating-voltage generators inductively coupled to the line loop for transmitting an operating current, normally of 25 Hz, to the ringer of the local station in response to a corresponding activating signal from the exchange. Such ringing-current generators, which may be of the toroidal-core type, are relatively costly and require elevated supply voltages, e.g. as high as 90 V.